In document distribution systems, the document to be transmitted is converted to millions of data bits per page. Document distribution systems may use coded information (CI) or non-coded information (NCI) to electronically transmit the document image. Whether the data is CI or NCI, it must be processed before it is transmitted. Processing may include data compression to reduce transmission time and data encryption for security purposes. Processing millions of data bits with a central processor to achieve these functions is wasteful and time-consuming.
It is much more efficient to use specialized peripheral devices working in parallel to perform the scan, compress, encrypt, transmit, receive, decrypt, decompress and print operations. An example of such a system is described in copending commonly-assigned patent application, Ser. No. 220,637, filed Dec. 29, 1980, now U.S. Pat. No. 4,454,575 entitled Shared Peripheral Processing System by K. A. Bushaw et al. In the Bushaw et al application, there is a supervisory processing unit to control the system and the peripheral devices, and there is a data processing unit or logic circuits in each peripheral device to process the data. This works well but lacks flexibility in configuring the terminal as a stand-alone scanner or printer separate from the peripheral devices performing the communication functions because each stand-alone box requires a supervisory processor.
Two processing units with time shared access to multiple peripheral devices is taught in U.S. Pat. No. 3,560,937 issued to R. P. Fischer on Feb. 2, 1971. However, the data is processed by the two processing units and not the peripheral devices. Further there is no intent to be able to reconfigure the system with some of the peripheral devices standing alone with their own processing unit separate from a systems processing unit.
In facsimile apparatus it is known to use a central processing unit to operate a facsimile terminal. Two examples are the R. E. Wernikoff et al U.S. Pat. No. 3,751,582 and the D. A. Perreault et al U.S. Pat. No. 3,914,537. Both of these patents use a single processor. Accordingly it would not be possible to breakoff stand-alone printers or stand-alone scanners from the communications apparatus because all these devices share one processing unit.